BURLINGTON, Vt./WASHINGTON (Reuters) - President Barack Obama vowed on Friday to forge ahead with tough sanctions on Iran, saying there was enough oil in the world market - including emergency stockpiles - to allow countries to cut Iranian imports.

In his decision, required by a sanctions law he signed in December, Obama said increased production by some countries as well as "the existence of strategic reserves" helped him come to the conclusion that sanctions can advance.

"I will closely monitor this situation to assure that the market can continue to accommodate a reduction in purchases of petroleum and petroleum products from Iran," he said in a statement.

Obama had been expected to press on with the sanctions to pressure Iran to curb its nuclear program, which the West suspects is a cover to develop atomic weapons but which Iran says is purely civilian.

The overt mention of government-controlled stockpiles may further stoke speculation that major consumer nations are preparing to tap their emergency stores this year.

"I do think it was interesting that it was laid out there," said David Pumphrey, an analyst at the Center for Strategic and International Studies.

"It was sort of like a reminder that yes, this is part of the tool kit," said Pumphrey, a former Energy Department official.

NO DECISION ON STRATEGIC RELEASE

Oil markets remain tight, the White House said. Surging gasoline prices have become a major issue in the presidential election campaign.

"A series of production disruptions in South Sudan, Syria, Yemen, Nigeria, and the North Sea have removed oil from the market," the White House said in a statement.

France is in talks with the United States and Britain on a possible release of strategic oil stocks to push fuel prices lower, French ministers said on Wednesday.

Senior Obama administration officials told reporters that the United States views releasing emergency stocks as an option, but said no decision has been made on specific actions.

Oil prices briefly rallied by about 70 cents on the announcement, but later reversed gains to end almost flat as traders turned mindful of the possible use of reserves.

"There's been a shift from focus on a threat (by Iran) to close the Strait of Hormuz to whether or not reserves are going to be released," said Dominick Caglioti, a broker at Frontier Trading Co. in New York.

PUTS IMPORTERS ON NOTICE

Going forward, Obama is required by law to determine every six months whether the price and supply of non-Iranian oil are sufficient to allow consumers to "significantly" cut their purchases from Iran.

The law allows Obama, after June 28, to sanction foreign banks that carry out oil-related transactions with Iran's central bank and effectively cut them off from the U.S. financial system.

"Today, we put on notice all nations that continue to import petroleum or petroleum products from Iran that they have three months to significantly reduce those purchases or risk the imposition of severe sanctions on their financial institutions," said Senator Robert Menendez, co-author of the sanctions law.

Obama can offer exemptions to countries that show they have "significantly" cut their purchases from Iran, and recently exempted Japan and 10 EU countries from the sanctions.

A senior administration official told reporters that talks continue with China, India, South Korea and other importers.

"Each day I think really we see a number of positive indicators from a broad range of countries," the official said, citing an announcement by Turkey on Friday that it would cut imports of oil from Iran by 10 percent as an example.

NEW SANCTIONS IN THE WORKS

Obama faces a delicate balancing act on Iran, leading up to November U.S. general election. On the one hand, he must show voters he is being tough on the Islamic state.

But with oil and gasoline prices surging in response to geopolitical risks, he must also avoid steps that would unduly rattle oil markets. That could threaten the global economy and hurt voters already angered by the rising cost of fuel.

Obama also faces pressure from some lawmakers in Congress who want to make sanctions on Iran even tighter. The House of Representatives has already passed additional sanctions, and a bill is pending in the Senate.

Senior administration officials briefing reporters declined comment on the proposed new sanctions.

"We welcome the president's determination and applaud the administration's faithful implementation of the Menendez-Kirk amendment," said a spokesman for Senator Mark Kirk, a Republican who has pushed for additional measures.

"To build on this momentum, we hope the Senate will consider amendments to the pending Iran sanctions bill that would continue to increase the economic pressure on the Iranian regime," Kirk's spokesman said.

(Additional reporting by Deborah Charles; Editing by Xavier Briand)